1. Field of the Invention
The invention relates to a method for conveying silicon chunks. The invention also relates to a vibrating conveyor.
2. Description of the Related Art
High-purity silicon is produced by chemical vapor deposition of a highly pure chlorosilane gas onto a heated substrate, for example. The silicon is in this case deposited in a polycrystalline fashion in the form of rods. A large part of the monocrystalline silicon required for the semiconductor industry is produced from these silicon rods by means of the Czochralski method.
In this method, a melting crucible is filled with silicon chunks. The fragmented silicon is melted, and a monocrystalline silicon ingot is pulled from the melt by means of a seed crystal.
The silicon chunks required for filling the melting crucible are obtained by comminuting the polycrystalline rods generated during the vapor deposition. For example, metal jaw or roll crushers, hammers or chisels are used as breaking tools.
After the contamination of the brittle silicon rods, undesirable particles and extraneous atoms may be detected on the sharp-edged surfaces of the chunks. The particles are generally dust, which is produced during the comminution of the silicon and during transport of the chunks; the extraneous atoms come in particular from the breaking tools.
These contaminants must be removed before the fragmented silicon is melted in the melting crucible. This is usually done by an etching treatment with acids or acid mixtures, which removes material, and subsequent washing with water.
The large specific surfaces of the sharp-edged chunks have serious disadvantages, and in particular give rise to                high acid consumption for treatments removing material,        high acid spreading through the superficially adhering acid film when transferring the fragmented silicon into a washing bath, with associated contamination of the washing water, and        undercut etching of the chunk edges.        
U.S. Pat. No. 6,375,011 B1 has therefore proposed a method for conveying fragmented silicon, in which the silicon chunks are conveyed over a conveyor surface, made of ultrapure silicon, of a vibrating conveyor.
In this case, sharp-edged silicon chunks are rounded when they are conveyed on the vibrating conveyor surface of a vibrating conveyor. The specific surfaces of the silicon chunks are reduced, and superficially adhering contaminants are ground off.
The fragmented silicon rounded by a first vibrating conveyer unit may be conveyed over a second vibrating conveyer unit. Its conveyor surface consists of ultrapure silicon plates arranged parallel, which are fixed by means of lateral fastening devices. The ultrapure silicon plates have passage openings, for example in the form of apertures. The conveyor edges, which serve to laterally delimit the conveyor surfaces, are likewise made of ultrapure silicon plates and, for example, are fixed by holders. The conveyor surfaces made of ultrapure silicon plates are supported by steel plates and optionally damping mats.
It has, however, been found that loosening and even fracture of the silicon cladding of the conveyor surface may occur during the operation of such vibrating conveyor units. Furthermore, there is therefore also a risk of product contamination during the conveying.
This gave rise to the object of the invention.